Gel-swellable particles and yarns in gel-filled buffer tubes

ABSTRACT

A fiber optic buffer tube containing fiber optic ribbons centrally located within the buffer tube and a gel compound surrounding the fiber optic ribbons. Disposed within the gel compound, between the walls of the buffer tube and the fiber optic ribbons are gel swellable yarns and/or particles. The gel swellable yarns/particles volumetrically expand when in contact with the gel compound causing greater force to hold the gel compound in place, especially when the fiber optic buffer is heated. The gel swellable yarns/particles also provide greater surface area and help to prevent the fiber optic ribbons from coming into contact with the walls of the buffer tube, thereby preventing signal attenuation problems.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to gel compounds within conduitsor buffer tubes and more specifically to the reduction of dripping ofthe gel compounds at higher temperatures.

2. Description of Related Art

Fiber optic cables have been used by the telecommunications industry fora number of years to transmit information at very high rates over longdistances. Fiber optic cables come in a variety of configurations,including: cables with a centrally located single buffer tube containingone or more optical fibers; cables with a plurality of buffer tubesstranded in a helical or alternating helical arrangement about a centralstrength member; and cables with slotted cores in which a plurality ofoptical fibers reside.

The buffer tubes within the ribbon cable generally contain one or morefiber optic ribbons centrally located within the buffer tube and a gelcompound surrounding the optical fiber ribbons. An example of this canbe seen in FIGS. 1-4. As shown in these figures, the fiber optic ribbons3 are centrally located within buffer tube 1. As can be further seenfrom FIGS. 1-4, a gel compound 2 surrounds the fiber optic ribbons 3.The gel compound 2 serves a number of purposes. One purpose is toprovide a cushioning media between the buffer tube 1 and the fiber opticribbons 3 to thereby prevent the fiber optic ribbons 3 from contactingthe sides of the buffer tube 1. The cushioning media dissipates radialcrushing force and in addition, the gel compound 2 provides delayedmotion response to the fibers under scanning bending loads. Such loadsoccur during the installation, when cables are pulled around the cornersof the ducts or over the sheaves. The same applies to the earlier stagesof manufacture when buffer tube 1 is bent over the sheaves and radiallycompressed by caterpillars. The artificial increase in the inertia ofthe ribbons 3 is provided by the viscous gel media and results in timedelay for fibers to accommodate the load and to move slower than in anon-gel media toward the tube walls 1. When the fiber optic ribbons 3contact the sides of the buffer tube 1, signal attenuation problemsoccur due to micro-bending and high stress. The gel compound 2 alsoserves to prevent exterior items from coming into contact with the fiberoptic ribbons 3 if the buffer tube 1 is penetrated. For example, the gelcompound 2 protects the fiber optic ribbons 3 from water that mightpenetrate the buffer tube 1.

Several problems occur in these conventional buffer tubes, especiallyones in which the buffer tube 1 diameter is large (for example, greaterthan 0.310 inches). First, when the temperature of the gel compound 2increases, the viscosity and yield stress of the gel compound 2decreases. If the yield stress of the gel decreases below a criticalvalue, the gel compound 2 may begin to flow. For example, if the buffertube 1 is physically positioned in a vertical manner, as shown in FIG.5, and the buffer tube 1 is heated, the gel compound 2 within the buffertube 1 may begin to flow towards the bottom of the buffer tube 1,leaving a cavity 4.

In more detail, as the temperature of the buffer tube 1 increases, thebuffer tube 1 expands, thereby increasing the diameter and length of thebuffer tube 1, according to the difference between the coefficient ofthermal expansion (“CTE”) of the buffer tube material 1 and gel compound2. As for the gel compound 2, as noted above, as its temperatureincreases, the viscosity and yield stress of the gel compound 2decreases. As shown in FIG. 5, gravity provides a downward force to thegel compound 2 while frictional forces (F1 and F2) with the tube wallare transmitted through the material by the yield stress of the gelcompound 2. Friction between the gel compound 2 and the buffer tube 1 islabeled F1 while the fiction between the gel compound 2 and the fiberoptic ribbons 3 is labeled F2. Consequently, as the temperature of thegel compound 2 increases, the yield stress of the gel compound 2decreases and the ability of the gel to transmit friction forces F1 andF1 through the gel compound 2 decreases. Since the downward force ofgravity remains constant during an increase in temperature of the gelcompound 2, when the temperature of the gel compound 2 increases, thedownward force of gravity on the material becomes greater than theupward force that can be transmitted through the material through theyield stress of the gel compound 2. As a result, the gel compound 2 mayflow downward.

Additionally, gel compound 2 may be “forced” out of the buffer tube 1when heated due to the difference between the CTE of the buffer tube 1and the CTE of the gel compound 2. As stated earlier, when heated, boththe buffer tube 1 and the gel compound 2 expand according to theirrespective CTE. If the CTE of the buffer tube 1 is less than the CTE ofthe gel compound 2, then the gel compound 2 expands more than the buffertube 1. Since the gel compound 2 is expansionally limited in the radialdirection by the buffer tube 1, if the gel compound 2 expands more thanthe buffer tube 1 when heated, the additional expansion of the gelcompound 2 is directed in the axial direction. As a result, gel compound2 is “forced” out of the ends of the buffer tube 1.

Once the gel compound 2 flows out of the buffer tube 1, it does notprovide adequate protection to the fiber optic ribbons 3. The fiberoptic ribbons 3 tend to contact the buffer tube walls 1, which in turnmay cause attenuation problems. Additionally, gel compound 2 flowing outof the buffer tubes 1 will flow into splice enclosures which make lateraccess to the closures problematic. Therefore, it is an object of thepresent invention to improve the compound flow performance of gel-filledfiber optic cables.

SUMMARY OF THE INVENTION

According to one aspect of the invention, optical fibers are provided ina conduit along with gel swellable material and a gel compound. In oneof the preferred embodiments, the conduit is a buffer tube.

More specifically, the present invention solves the above-describedproblems and limitations by placing gel swellable yarns and/or gelswellable particles within the gel-filled conduits or buffer tubes. Thegel swellable yarns and particles, when in contact with the gel compound(especially when heated), begin to swell. As a result, theyarns/particles provide many beneficial effects. First, the gelswellable yarns/particles absorb the lower viscosity component of thegel compound, thereby reducing the likelihood of oil separation. Second,the swelling of the yarns/particles push outward on the gel compound,thereby increasing the friction forces F1 and F2 that help to hold thegel compound in place. Third, the yarns/particles themselves providesurface area for the gel compound to contact which in turn providesadditional friction forces that help to keep the gel compound fromflowing downward. Fourth, the swelling of the yarns/particles helps tocompensate for the expansion of the buffer tube walls due to theincrease in temperature by making the expansion and CTE of the gel-yarnor gel-particle system closer to that of the buffer tube material.

In a preferred embodiment of the present invention, gel swellable yarnshaving whiskers are disposed between the fiber optic ribbon stacks andthe walls of the buffer tube. The gel swellable yarns vary in size andsurround the fiber optic ribbon stacks.

In another embodiment of the present invention, gel swellable particleshaving whiskers are embedded in the gel compound. The gel swellableparticles are sub-millimeter sized and preferably made of apolyolefin-type material. The gel swellable particles are mixed with thegel compound before the buffering step.

In yet another embodiment of the present invention, both gel swellableyarns and particles are embedded in the gel compound.

Further objects, features and advantages of the invention will becomeapparent from a consideration of the following description and theappended claims when taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The above aspects of the present invention will become more apparent bydescribing in detail embodiments thereof with reference to the attacheddrawings, in which:

FIG. 1 is a plan view of a conventional buffer tube;

FIG. 2 is a side view of a conventional buffer tube with a transparentfront of the buffer tube;

FIG. 3 is a side view of a conventional buffer tube;

FIG. 4 is a side view of a conventional buffer tube taken along theIV—IV line of FIG. 1;

FIG. 5 is side view of a conventional buffer tube taken along the IV—IVline of FIG. 1 showing the forces acting on the gel compound when thetemperature of the buffer tube is increased;

FIG. 6 is a perspective view of a buffer tube according to a preferredembodiment of the present invention;

FIG. 7 is a side view of the buffer tube of FIG. 6 showing the forcesacting on the gel compound when gel swellable yarns are embedded in thegel compound;

FIG. 8 is a plan view of the buffer tube of FIG. 6;

FIG. 9 is an overhead view of another embodiment of the presentinvention when gel swellable particles are embedded in the gel compound.

FIG. 10 is a chart showing the effects of temperature on the swelling ofPolyethylene; and

FIG. 11 is a chart showing the effect of material type and density onthe swelling of the materials at 85° C.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, embodiments of the present invention will be described indetail with reference to the attached drawings. The present invention isnot restricted to the following embodiments, and many variations arepossible within the spirit and scope of the present invention. Theembodiments of the present invention are provided in order to morecompletely explain the present invention to one skilled in the art.

Referring to FIG. 6, the present invention solves many of the problemscreated when a buffer tube 1 containing a single ribbon or single stackof ribbons 3 centrally located and surrounded by gel compound 2, isheated. The buffer tube 1 can be made of any type material and can beany shape. Generally, the buffer tube 1 is cylindrical in shape. Thefiber optic ribbons 3 can be assembled in stacks (as shown) or can beindividual if necessary. The gel compound 2 is also not limited in anymanner.

The present invention, as shown in FIG. 6, embeds gel swellable yarns 5in the gel compound 2, between the walls of the buffer tube 1 and thefiber optic ribbon stack 3. The gel swellable yarns 5 can be disposed ina number of ways. For example, the gel swellable yarns 5 can run axiallyparallel to the fiber optic ribbon 3 or even be wrapped around the fiberoptic ribbon 3 in a helical manner. The gel swellable yarns 5 do nothave to be evenly dispersed within the buffer tube 1. For example, thegel swellable yarns 5 can be places closer to the buffer tube walls 1than to the fiber optic ribbons 3. Although FIG. 6 shows only one gelswellable yarn 5, any number of yarns can be used. As shown in FIG. 8,the size and shape of the yarns can vary as well as the type. Forexample, although the figures show the yarns 5 with whiskers, thepresent invention can be practiced using gel swellable yarns 5 with orwithout whiskers. Gel swellable yarns 5 can also be replaced by gelswellable tape or any other material that volumetrically expands when incontact with gel compound 2.

As described earlier, a problem arises when the buffer tube 1 and gelcompound 2 become heated. By adding the gel swellable yarns 5, theproblem of the gel compound 2 flowing downward can be diminished. Asshown in FIG. 7, adding gel swellable yarns 5 to the buffer tube 1results in two additional upward forces F3, F4 that help prevent the gelcompound 2 from running downward.

The addition of the gel swellable yarns 5 increases the amount ofsurface area with which the gel compound 2 may contact. The additionalsurface area results in two additional forces F3, F4 that act upon thegel compound 2. As a result, more upward forces can be transmitted tocompound 2.

Additionally, by selecting yarn and/or particles having a CTE which isless than the CTE of the gel compound 2, the CTE of the gel-yarn orgel-particle system is lowered. In fact, it is possible to select yarnsand particles having a negative CTE (i.e. yarns/particles thatvolumetrically contract when heated). In a preferred embodiment, yarnsand/or particles are selected in such a manner that the resulting CTE ofthe gel-yarn or gel-particle system matches or is substantiallyequivalent to the CTE of the buffer tube 1. Consequently, when heated,both the buffer tube 1 and the gel-yarn/gel-particle system expand bythe same amount. As a result, gel compound 2 is not “forced” out of thebuffer tube 1 in the axial direction.

Equations governing the flow of gels within vertical tubes can bedeveloped based on the following assumptions:

-   -   Laminar, axisymmetric, steady state flow    -   Incompressible, homogeneous fluid (no oil separation/single        phase)    -   No end effect    -   No slip condition    -   Bingham model is applicable to the Non-Newtonian water-blocking        gel.

By performing the momentum balance on the controlled volume as shown inFIG. 1, and applying the above assumptions, the following equation canbe obtained: $\begin{matrix}{{\frac{\mathbb{d}\quad}{\mathbb{d}r}\left( {r\quad\tau_{rz}} \right)} = {\frac{P_{0} - P_{L} - {\rho\quad{gL}}}{L}r}} & (1)\end{matrix}$Where, τ_(rz) is the shear stress in z direction at a radius r; ρ is thedensity of the fluid; L is the length of the tube; P₀ is the pressure atI=0; P_(L) is the pressure at I=L.

Boundary conditions for the above equation are as follows:At r=0, τ_(rz)=Finite  (2)At r=R, v_(z=0)(no slip condition)  (3)For a fluid, τ_(rz) can be expressed by the following equations usingthe Bingham model:τ_(rz)=τ₀−μ₀ dv _(z) /dr for r ₀ ≦r≦R  (4)τ_(rz)=τ₀−μ₀ for 0≦r≦r ₀  (5)Where r ₀=2Lτ ₀/(P ₀ −P _(L) +ρgL)  (6)Equation 1 can be solved along with Equations (2)-(6) for the volumetricflowrate, Q. Q is given by: $\begin{matrix}{Q = {\frac{\pi\quad\tau_{0}}{\mu_{0}}\left\lbrack {{\frac{1}{4A}\left( {R^{4} - r_{0}^{4}} \right)} - {\frac{1}{3}\left( {R^{3} - r_{0}^{3}} \right)}} \right\rbrack}} & (7)\end{matrix}$Where r ₀=2Lτ ₀/(P ₀ −P _(L) +ρgL)  (8)

To incorporate the effects of thermal expansion differences of the geland tube materials, it is necessary to calculate the change in volumeassociated with these differences. The change in volume is given by:ΔV _(T) =ΔV _(gel@T) −ΔV _(tube@T)  (9)Where ΔV_(gel@T)=Alβ_(gel)ΔT  (10)ΔV_(tube@T)=Alβ_(tube)ΔT  (11)

-   -   ΔV_(T) is the extruded volume of gel at temperature, T.    -   ΔV_(gel@T) is the volume change of the gel at temperature, T.    -   ΔV_(tube@T) is the volume change of the tube at temperature, T    -   A is the area of the inside of the tube.    -   β_(gel) is volumetric coefficient of thermal expansion of the        gel.    -   β_(tube) is volumetric coefficient of thermal expansion of the        tube.    -   ΔT is the difference between the filling and test temperatures.        After substituting and rearranging, the equation becomes        ΔV _(T) =Al _(o) ΔT(β_(gel)−β_(tube)).  (12)

To predict the amount of gel flow to be extruded due to differences inthermal expansion between the gel and tube, one simply rearranges thedensity equation to obtain:Mass(g)=ΔV_(Tρgel@T)  (13)

Now that the volume and mass of the extruded gel at some temperature, T,is known, it is possible to calculate the yield stress required by thegel material to prevent drip. This can be accomplished by the followingrelationship assuming that the change in the radius due to thermalexpansion is small.τ₀ ′=F/A=mg/A  (14)Where,

-   -   τ₀′ is the stress associated with the extruded gel; F represents        a force; A is the area of the inside of the tube, m is the mass        of the extruded gel at temperature T; g is the acceleration due        to gravity which equals 980 cm/s².

The minimum yield stress value of the gel for a “no flow” condition canbe predicted by the greater of the two values obtained from τ₀ and τ′₀.

Also, since the gel swellable yarns 5 occupy some of the volume insidethe buffer tube 1, less gel compound 2 may consequently be used. Usingless gel compound 2 results in at least two beneficial effects. First,since gel compound 2 is expensive, using less means the cost ofmanufacturing the fiber optic cable is decreased. Second, since theforce acting in the downward direction (i.e. gravity) is a function ofthe mass of the gel compound 2, replacing some of the gel compound withyarns having less mass than the gel compound decreases the downwardforce due to gravity. A decrease in the force of gravity means that lessupward force (i.e. friction forces F1, F2, F3, and F4) is needed to keepthe gel compound 2 from running down the fibers. When the gel compound 2is held in place, it prevents the fiber optic ribbons 3 from contactingthe walls of the buffer tube 1 and also prevents other materials (i.e.water) that might penetrate the buffer tube 1 from contacting the fiberoptic ribbons 3.

These same principles hold true when gel swellable particles 6 areembedded in the gel compound 2 as shown in FIG. 9. When the gelswellable particles 6 come into contact with the gel compound 2, the gelswellable particles 6 begin to volumetrically expand. This volumetricexpansion of the gel swellable particles 6, much like the expansion ofthe gel swellable yarns 5, pushes the gel compound 2 against the buffertube wall 1 and the fiber optic ribbons 3 which in turn increases theupward friction forces. The gel swellable particles 6 also increase thesurface area that the gel compound contacts, thereby creating additionalfriction forces that act in the upward direction. Finally, the gelswellable particles 6 occupy some of the volume inside the buffer tube1, which decreases the amount of gel compound 2. This decrease thegravitational force that acts on the gel compound in the downwarddirection.

The gel swellable particles 6 are not limited by shape or size or thenumber or amount used within the buffer tube. Several polyolefincopolymers suitable for use as gel swellable particles or for use withinthe yarns in the present invention, have been identified. FIG. 10depicts the swelling (% swelling on the vertical axis) of polyethyleneas a function of temperature (Room Temperature, 60° C., and 85° C.) anddensity, and FIG. 11 depicts the effect of material type and density onswelling at 85° C., where PE is a polyethylene material and PP is apolypropylene material. As shown in FIG. 10, the swellability ofdifferent material densities at 85° C. can be anywhere from moderatelyswelled to totally miscible. It is desirable to have a gel-swellablematerial where the swellability varies as a function of temperature.Further, it is desirable to have the material chosen for thegel-swellable particles or yarns be softer than that used for the outerjacket or tube 10, which is normally a polypropylene copolymer typematerial, which typically has a density greater than 0.900 g/c³.Typically, swelling of the jacket materials at 85° C. reaches a maximumvalue of less than 3% with a polyolefin oil based gel. (Thecharacteristics of such a gel are discussed in U.S. Pat. No. 6,085,009).As shown in FIG. 11, both polethylenes and polypropylenes with a densitybelow about 0.89 g/c³ are substantially swellable with a polyolefinbased gel. Therefore, when this type of material is used for thegel-swellable yarns or particles, the gel-swellable layer will absorbsome of the gel while the buffer tube or jacket 10 would remainsubstantially unaffected.

The gel-swellable materials include ethylene-octene copolymers,propylene-ethylene copolymers, ethylene-octene-propylene terpolymers orother similar copolymers or terpolymers. Other suitable materials usefulclass of compounds for such an application, which are highly swellable,are ethylene-styrene interpolymers. In the preferred embodiment,low-density polyethylene, with a density less than 0.90 g/cc is used asthe gel-swellable material.

Further, gel swellable particles 6 having whiskers provide even moresurface area but gel swellable particles 6 without whickers may also beused. Additionally, any combination of gel swellable yarns, tapes andparticles may be used. The yarns may also be used to “drag” the gelcompound 2 into the buffer tube 1 which speeds manufacturing of thebuffer tubes 1. Finally, the gel swellable yarns may be oriented axiallyparallel or disposed helically around the fiber optic ribbons 3.

The buffer tubes of the present invention can be made in a number ofways. The yarns most likely will be applied during thebuffering/stranding process of the ribbon buffer tubes. The yarns arewound onto a delivery spool and then delivered along with the otheroptical units into the tube while the polymer is being extruded. Thatis, ribbons are “stranded” and then “buffered” usually in a singleprocess step. These terms, (stranded and buffered) are commonly used formanufacturing optical units in the industry. The advantages to thisare 1) being able to control yarn tensions (which are critical tomaintain desired stack integrity) and 2) applying them in the “stacks”“final” formation just prior to entering the buffer tube. Also, itallows you to apply them in the desired helical formation of the“stack”. The “stack” can then orient itself in an ideal centerposition—cushions will help to center the stack within the polymer tube,which can prevent attenuation degradation due to the potential for theoptical units to engage the tube wall.

The buffer tubes of the present invention can be made in a number ofways. Typically, an assembled stack of fiber ribbons is pulled through adie. Gel compound is injected in the die (from the inside) and a hotthermoplastic material is extruded over the gel-stack system (from theoutside) to form a buffer tube with gel and ribbons inside. The buffertube is then moved through a water-cooling channel and wound on thereel. In a preferred embodiment, the gel swellable yarns 5 are pulledwith the assembled stack of fiber ribbons through the die.

The above description of the preferred embodiments has been given by wayof example. From the disclosure given, those skilled in the art will notonly understand the present invention and its attendant advantages, butwill also find apparent various changes and modifications to thestructures and methods disclosed. It is sought, therefore, to cover allsuch changes and modifications as fall within the spirit and scope ofthe invention, as defined by the appended claims, and equivalentsthereof.

1. A fiber optic buffer tube comprising: at least one optical fiberhaving a coefficient of thermal expansion disposed within said buffertube; gel compound having a coefficient of thermal expansion disposedwithin said buffer tube, wherein said gel compound is disposed betweensaid at least one optical fiber and said buffer tube; and at least onegel swellable material having a coefficient of thermal expansiondisposed within said buffer tube.
 2. The fiber optic buffer tube ofclaim 1, wherein said at least one optical fiber is circumferentiallyarranged within said buffer tube.
 3. The fiber optic buffer tube ofclaim 1, wherein said at least one optical fiber is a fiber opticribbon.
 4. The fiber optic buffer tube of claim 1, wherein said at leastone optical fiber is a bundle of fibers.
 5. The fiber optic buffer tubeof claim 1, wherein said at least one gel swellable material is gelswellable yarn.
 6. The fiber optic buffer tube of claim 1, wherein saidat least one gel swellable material is gel swellable particles.
 7. Thefiber optic buffer tube of claim 5, wherein said gel swellable yarn haswhiskers.
 8. The fiber optic buffer tube of claim 6, wherein said gelswellable particles have whiskers.
 9. The fiber optic buffer tube ofclaim 1, wherein the coefficient of thermal expansion of said at leastone gel swellable material is less than the coefficient of thermalexpansion of said gel compound.
 10. The fiber optic buffer tube of claim1, wherein the coefficient of thermal expansion of said at least one gelswellable material is less than the coefficient of thermal expansion ofsaid buffer tube.
 11. The fiber optic buffer tube of claim 1, whereinsaid gel compound and said at least one gel swellable material form agel system having a coefficient of thermal expansion, and wherein thecoefficient of thermal expansion of said gel system is matched to thecoefficient of thermal expansion of said buffer tube.
 12. The fiberoptic buffer tube of claim 1, wherein said at least one gel swellablematerial includes a first type gel swellable material and a second typegel swellable material; and wherein said first type gel swellablematerial is different than said second type gel swellable material. 13.The fiber optic buffer tube of claim 12, wherein said first type gelswellable material is gel swellable yarn and said second type gelswellable material is gel swellable particles.
 14. The fiber opticbuffer tube of claim 12, wherein said first type gel swellable materialis gel swellable yarn and said second type gel swellable material is gelswellable tape.
 15. The fiber optic buffer tube of claim 12, whereinsaid first type gel swellable material is gel swellable tape and saidsecond type gel swellable material is gel swellable particles.
 16. Thefiber optic buffer tube of claim 1 wherein said at least one gelswellable material volumetrically expands when heated.
 17. The fiberoptic buffer tube of claim 1 wherein said at least one gel swellablematerial volumetrically contracts when heated.
 18. The fiber opticbuffer tube of claim 5, wherein said gel swellable yarn is arrangedaxially parallel to said at least one optical fiber.
 19. The fiber opticbuffer tube of claim 5, wherein said gel swellable yarn is helicallydisposed around said at least one optical fiber.
 20. A method ofimproving gel compound flow performance of a gel-filled fiber opticbuffer tube having a coefficient of thermal expansion and having atleast one optical fiber, comprising: embedding at least one gelswellable material having a coefficient of thermal expansion within saidbuffer tube, wherein said gel compound has a coefficient of thermalexpansion.
 21. The method of improving gel compound flow performance ofa gel-filled fiber optic buffer tube having at least one optical fiberof claim 20, wherein said at least one optical fiber iscircumferentially arranged within said buffer tube.
 22. The method ofimproving gel compound flow performance of a gel-filled fiber opticbuffer tube having at least one optical fiber of claim 20, wherein saidat least one gel swellable material is gel swellable yarn.
 23. Themethod of improving gel compound flow performance of a gel-filled fiberoptic buffer tube having at least one optical fiber of claim 20, whereinsaid at least one gel swellable material is gel swellable particles. 24.The method of improving gel compound flow performance of a gel-filledfiber optic buffer tube having at least one optical fiber of claim 20,wherein said gel swellable yarn has whiskers.
 25. The method ofimproving gel compound flow performance of a gel-filled fiber opticbuffer tube having at least one optical fiber of claim 21, wherein saidgel swellable particles have whiskers.
 26. The method of improving gelcompound flow performance of a gel-filled fiber optic buffer tube havingat least one optical fiber of claim 20, wherein the coefficient ofthermal expansion of said at least one gel swellable material is lessthan the coefficient of thermal expansion of said gel compound.
 27. Themethod of improving gel compound flow performance of a gel-filled fiberoptic buffer tube having at least one optical fiber of claim 20, whereinthe coefficient of thermal expansion of said at least one gel swellablematerial is less than the coefficient of thermal expansion of saidbuffer tube.
 28. The method of improving gel compound flow performanceof a gel-filled fiber optic buffer tube having at least one opticalfiber of claim 20, wherein said gel compound and said at least one gelswellable material form a gel system having a coefficient of thermalexpansion, and wherein the coefficient of thermal expansion of said gelsystem is matched to the coefficient of thermal expansion of said buffertube.
 29. The method of improving gel compound flow performance of agel-filled fiber optic buffer tube having at least one optical fiber ofclaim 20, wherein said at least one gel swellable material includes afirst type gel swellable material and a second type gel swellablematerial; and wherein said first type gel swellable material isdifferent than said second type gel swellable material.
 30. The methodof improving gel compound flow performance of a gel-filled fiber opticbuffer tube having at least one optical fiber of claim 29, wherein saidfirst type gel swellable material is gel swellable yarn and said secondtype gel swellable material is gel swellable particles.
 31. The methodof improving gel compound flow performance of a gel-filled fiber opticbuffer tube having at least one optical fiber of claim 29, wherein saidfirst type gel swellable material is gel swellable yarn and said secondtype gel swellable material is gel swellable tape.
 32. The method ofimproving gel compound flow performance of a gel-filled fiber opticbuffer tube having at least one optical fiber of claim 29, wherein saidfirst type gel swellable material is gel swellable tape and said secondtype gel swellable material is gel swellable particles.
 33. The methodof improving gel compound flow performance of a gel-filled fiber opticbuffer tube having at least one optical fiber of claim 20, wherein saidat least one gel swellable material volumetrically expands when heated.34. The method of improving gel compound flow performance of agel-filled fiber optic buffer tube having at least one optical fiber ofclaim 20, wherein said at least one gel swellable materialvolumetrically contracts when heated.
 35. The method of improving gelcompound flow performance of a gel-filled fiber optic buffer tube havingat least one optical fiber of claim 22, wherein said gel swellable yarnis arranged axially parallel to said at least one optical fiber.
 36. Themethod of improving gel compound flow performance of a gel-filled fiberoptic buffer tube having at least one optical fiber of claim 22, whereinsaid gel swellable yarn is helically disposed around said at least oneoptical fiber.
 37. A method of forming an optical fiber membercomprising the following steps: providing at least one optical fiberhaving a coefficient of thermal expansion; providing a gel compoundhaving a coefficient of thermal expansion along said optical fiber;providing at least one gel swellable material having a coefficient ofthermal expansion along said optical fiber; and forming a conduit aroundsaid optical fiber, said gel compound, and said gel swellable materialsuch that when said gel swellable material contacts said gel compound,said gel swellable material expands volumetrically within said conduit.38. The method of forming an optical fiber member of claim 37, whereinsaid gel swellable material has whiskers.
 39. The method of forming anoptical fiber member of claim 38, further comprising: dragging said gelinto said conduit using said gel swellable material.